Tori Foster
Pages 69-90
(2.6 – Changes)Climax Communities
2.6.7 – Describe factors affecting the nature of climax communities.
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Ecosystem stability refers to how well an ecosystem is able to cope with changes

Most systems contain inbuilt checks and balances – negative feedback systems – which
they need to be self-sustaining.

Ecosystems in later stages of succession are likely to be more stable, because more
negative feedback systems have developed, and food webs are more complex.
o
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A species can turn to an alternative food source if one species is reduced.
Features of a climax community:
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Greater biomass
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Higher levels of species diversity
o
More favorable soil conditions (ex: greater organic content)
o
Better soil structure (greater water retention)
o
Lower pH
o
Taller and longer-living plant species
o
More K-strategists or fewer r-strategists
o
Greater community complexity and stability
o
Greater habitat diversity
o
Steady-state equilibrium
o
Lowland tropical rainforest in South-East Asia is a climax community.
Plagioclimax
o
Climatic and edaphic (relating to soil) factors determine the nature of a climax
community
o
Human factors often disturb this process, and a climax community may not be
reached
o
Interrupted succession is called plagioclimax
o
Footpath erosion, agriculture, hunting, clearance, burning, and grazing stop
succession
o
Deforestation is having a major impact on tropical rainforests, one of the most
diverse biomes
o
Examples:

large parts of the UK were once covered by deciduous forests, which
were cleared to supply timber and for agriculture from the Middle Ages
onwards. Heather now dominates the plant community and sheep
grazing prevents re-growth of woodland by killing saplings.

Deforestation in Borneo may cause the extinction of the Bornean
orangutan, a species endemic to the island

Deforestation in tropical rainforests in Brazilian Amazon basin
2.7 Measuring changes in the system
2.7.1 Describe and evaluate methods for measuring changes in abiotic and biotic components of
an ecosystem along an environmental gradient.

Ecological gradients are found where two ecosystems meet (ex: beaches) or where an
ecosystem suddenly ends (ex: forest edges)

Both biotic and abiotic factors vary with distance and form gradients in which trends can
be recorded.

Sampling techniques used for ecological gradients are based on the quadrant method,
and easily done on vegetation and immobile or slow-moving animals.

However, environmental variable change along the gradient, and instead a transect is
used.
o
Line transect – tape measure laid out in the direction of the gradient; all
organisms touching the tape are recorded.
o
Belt transect – a band of a chosen width laid along the gradient
o
Continuous transect – the whole transect is sampled
o
Interrupted transect – samples are taken at points of equal distance along the
gradient

Transects should be carried out at the same time of day, so abiotic variables are
comparable, and taken ether as close together in time as possible or throughout the
year due to seasonal fluctuations.

Transects should be repeated multiple times.
2.7.2 Describe and evaluate methods for measuring changes in abiotic and biotic components of
an ecosystem due to a specific human activity.
Nuclear contamination following the Chernobyl disaster

Four nuclear reactors were located at Chernobyl, one of which exploded in April 1986.

A combination of factors and circumstances contributed, including design drawbacks
with the reactor and human error, as a result of poor supervision.

Two non-nuclear explosions in quick successions occurred due to an increase in thermal
power. These penetrated the nuclear reactor and blew the roof off, releasing debris and
radionuclides, which were normally contained in the reactor core. Concrete, graphite,
and other debris were heated to very high temperatures and released into the
atmosphere. Radionulides were released for nearly ten days and distributed widely
across western Europe., contaminating soil, plants, animals, and foodstuffs.
- Response:

Firefighters from the nearby town of Pripyat arrived. It took over 3 hours to extinguish
all the main fire sites, with the exception of the fire in the core of the reactor, which was
extinguished by dumping 5000 tonnes of sand, lead, and clay by helicopter.

31 deaths, 200 cases of radiation burns, and health effects are still emerging.
o
An increase in throat cancers has been recorded

A sarcophagus was built around the exposed reactor to isolate it, but difficult working
conditions caused gaps in the container, which are regularly monitored for radiation.

Everyone living within 30km of the reactor was evacuated and decontamination began
o
All soil to a depth of 15 cm was removed, and all buildings were cleaned. Later
found to be of limited effectiveness.
o
140 dykes and dams were built to prevent radionuclides seeping into rivers and
the Kiev reservoir
Methods of measuring changes in abiotic and biotic components

Satellite images – very reliable, covers a large area, and allows us to see change over
time.

Excavations and mining

The size of landforms created or destroyed can be measured by estimating rates
of erosion – measured by the lowering of the surface, or the volume carried
away by rivers, or the volume of material removed

Excavation and dumping involve the mining of sediments, the tipping of waste
material, and the subsidence such activities create.

The most important effect has been the dumping of waste material.

Environmental destruction caused by strip mining exceeds any other direct form
of impact that humans have on landforms. By 1922 it was estimated that as
much 31 billion tones of rock had been removed from Britain as a result of
human activity.

The demand for mineral resources continues to increase.
2.7.3 Describe and evaluate the use of Environmental Impact Assessments.
Environmental Impact Assessments

Demand for resources, new housing, new energy supplies, and for new
transport links are inevitable, but before any development project gets
permission to begin an Environmental Impact Assessment must be carried out.

EIAs establish the impact of the project on the environment.


Predicts impacts on habitats, species, and ecosystems.

Helps decision makers decide if the development should go ahead.
First stage: carry out a baseline study including:

Habitat type and abundance – record total area of each habitat type

Species list – record number of species present

Species diversity – estimate abundance of each species and calculate diversity of
the community

List of endangered species

Land use – assess land use type and use coverage

Hydrology – assess hydrological conditions in terms of volume, discharge, flows,
and water quality

Human population – assess present population

Soil – quality, fertility, and pH

Difficult to put together a complete baseline study, due to lack of data.

Environmental impact prediction is speculative, because natural systems are so complex

Whether a government takes the advice the EIAs offer is up to the environmental
philosophy of the government.
Case Study: Three Gorges Dam, Yangtze River

The largest hydroelectric dam development in the world
 Project engineers predicted that the dam could generate an eighth of the country’s
electricity
o
No harmful greenhouse gases

Reduced seasonal flooding and increased economic development along the edges of the
new reservoir

The EIA determined that there were 47 endangered species in the area, including the
Chinese river dolphin and Chinese sturgeon

The physical barrier of the dam would interfere with fish spawning and, in combination
with pollution, would have a serious impact on the fishing economy

Dam would flood 13 cities, 140 towns, 1352 villages, and 100,000 acres of china’s most
fertile land

4 million people would have to be resettled by 2020

Risk of landslides and increased chance of earthquakes

Less sedimentation reaching East China Sea, reducing fertility of the land in that area

The overall view of the people responsible for the development was that the positive
impact on the environment and national economy outweighed any negative impact
Chapter 3 – Human Population, Carrying Capacity, and Resource Use
3.1 Population Dynamics
3.1.1 Describe the nature and explain the implications of exponential growth in human
populations.
Exponential growth in human populations

The world’s population doubled between 1802 and 1922, 1922 and 1959, 1959 and
1974.

Up to 95% of population growth is occurring in LEDCs.

Growth has slowed since 1999.
o
In 1990, women were, on average, giving birth to 3.3 children in their lifetime.
o
By 2002, the figure had dropped to 2.6 children, slightly above replacement
level
o
If this trend continues, the level of fertility will drop below replacement level
before 2050
o
Projections also suggest that AIDS (which has killed 20 million people in the past
20 years) will lower the average life expectancy at birth to 30 years in some
countries.


The impact of exponential growth is that a huge amount of extra resources are needed
to feed, house, clothe, and look after the increasing number of people
o

Greatest impact in developing countries
However, resource use in LEDCs, where population growth is much higher, is
much lower than in MEDCs, where population growth is slower.
A shrinking population would mean an increase in the number of elderly people in the
world. Life expectancy is increasing but social security systems are not
3.1.2 Calculate and explain, from given data, the values of crude birth rate, crude death rate,
fertility, doubling time, and natural increase rate.
Calculating important rates

Birth rates –
o
Crude birth rate (CBR) – births per thousand, not taking into account age and
sex structure of a population
o

Standardized birth rate – gives birth rate for a region on the basis that its age
composition is the same as a whole country
Fertility
o
Total fertility rate(TFR) – average number of births per woman of child-bearing
age
o
General fertility rate (GFR) – number of births per thousand women aged 15-49
years
o
Age-specific fertility rate (ASBR) – number of births per thousand women of any
specified year groups
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In general, the highest fertility rates are found among the poorest countries

In MEDCs, birth rates and fertility rates have fallen
Changes in fertility are a combination of socio-cultural and economic factors

Level of education and material ambition – the higher the level of parental education,
the fewer the children. Poor people with limited resources or ambition often have large
families.

Poilitcal factors and family planning – most governments in LEDCs have introduced
programs aimed at reducing birth rates, but effectiveness depends on
o
A focus on general family planning, not just birth control
o
Investing sufficient finance in the schemes
o
Working in consultation with the population

Economic prosperity – as gross domestic income increases, total fertility rate generally
decreases. As gross national product per capita increases, birth rate decreases

The need for children – high infant mortality rates increase the pressure on women to
have more children – “replacement births.” In some agricultural societies, parents have
larger families to provide labor for the farm and security in old age.
Doubling times

The length of time it takes for a population to double in size.
Death rates

Crude death rate (CDR) – number of deaths per thousand people in a population

Infant mortality rate (IMR) – total number of deaths of children aged under 1 year per
1000 live births

MEDCs have lower death rates due to better nutrition, healthcare, and environmental
conditions, and very high life expectancies.

In LEDCs, high death rates and low life expectancies are still common.
Variations in mortality rates occur due to:

Age structure – populations with a large proportion of young people would have lower
death rates, while those with a large proportion of elderly would have higher death
rates.

Social class – poorer people within any population have higher mortality rates than the
more affluent. In some countries this is also reflected in racial groups.

Occupation – certain occupations are hazardous, and some diseases are linked to
specific occupations

Place of residence – in urban areas, mortality rates are higher in areas of relative
poverty, due to overcrowding, pollution, high population densities and stress. In rural
areas where there is widespread poverty and limited farm productivity, mortality rates
are high

Child mortality and IMR – high IMRs are found in poorest countries; causes of infant
deaths are often preventable; IMRs are low where there is a safe water supply and
adequate sanitation, housing, healthcare, and nutrition.
Natural increase

Calculated by subtracting CDR from CBR.
3.1.3 Analyse age/sex pyramids and diagrams showing demographic transition models.
Population pyramids

Tell us a great deal about age and sex structure of a population:
o
A wide base indicates a high birth rate
o
Narrowing base indicates lowering birth rate
o
Straight or near-vertical sides reveal a low death rate
o
Concave slopes characterize high death rates
o
Bulges in the slope suggest high rates of immigration
o
Deficits in slope indicate emigration or age-specific or sex-specific deaths
(epidemics, war)
3.1.4 Discuss the use of models in predicting the growth of human populations.
Demographic transition model – figure 3.7, on page 90
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Stage 1 – High and variable
o
Birth and death rates high and variable
o
Population growth fluctuates
o
No countries, only some indigenous tribes still at this stage
Stage 2 – Early expanding
o
Birth rate remains high but the death rate comes down rapidly
o
Population growth is rapid
o
Afghanistan, Sudan, and Libya are at this stage
Stage 3 – Late expanding
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Birth rate drops and the death rate remains low
o
Population growth continues but at a smaller rate
o
Brazil and Argentina are at this stage
Stage 4 – Low and variable
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Birth rates and death rates are low and variable
o
Population growth fluctuates
o
UK and most developed countries are at this stage
Stage 5 – Low declining
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Birth rate is lower than the death rate
o
Population declines
This model is based on data from only England, Wales, and Sweden.